Magnetic recording medium with high density thin dual carbon overcoats

ABSTRACT

A magnetic recording medium is formed with dual carbon-containing protective layers having a combined thickness of less than about 100 Å with high corrosion resistance and superior magnetic performance. Embodiments of the present invention include sputter depositing a first protective layer of hydrogenated carbon at a density of at least 1.9 while applying a DC bias of about 250V to about 400V to the substrate, and sputter depositing a second protective layer comprising nitrogen-doped hydrogenated carbon on the first protective layer.

RELATED APPLICATIONS

This application claims priority from provisional patent applicationSer. No. 60/129,190 filed Apr. 14, 1999, entitled “DUAL LAYER CARBONWITH PROGRAMMABLE BIAS SCHEME FOR MAGNETIC DATA STORAGE DISKSAPPLICATION,” the entire disclosure of which is hereby incorporated byreference herein.

TECHNICAL FIELD

The present invention relates to magnetic recording media, particularlyrotatable magnetoresistance (MR) or giant magnetoresistance (GMR)recording media, such as thin film magnetic disks cooperating with amagnetic transducer head. The present invention has particularapplicability to high areal density magnetic recording media designedfor drive programs having a reduced flying height, orpseudo-contact/proximityrecording.

BACKGROUND ART

Thin film magnetic recording disks and disk drives are conventionallyemployed for storing large amounts of data in magnetizable form. Inoperation, a typical contact start/stop (CSS) method commences when adata transducing head begins to slide against the surface of the disk asthe disk begins to rotate. Upon reaching a predetermined high rotationalspeed, the head floats in air at a predetermined distance from thesurface of the disk where it is maintained during reading and recordingoperations. Upon terminating operation of the disk drive, the head againbegins to slide against the surface of the disk and eventually stops incontact with and pressing against the disk. Each time the head and diskassembly is driven, the sliding surface of the head repeats the cyclicoperation consisting of stopping, sliding against the surface of thedisk, floating in the air, sliding against the surface of the disk andstopping.

For optimum consistency and predictability, it is necessary to maintaineach transducer head as close to its associated recording surface aspossible, i.e., to minimize the flying height of the head. Accordingly,a smooth recording surface is preferred, as well as a smooth opposingsurface of the associated transducer head. However, if the head surfaceand the recording surface are too smooth, the precision match of thesesurfaces gives rise to excessive stiction and friction during the startup and stopping phases, thereby causing wear to the head and recordingsurfaces, eventually leading to what is referred to as a “head crash.”Thus, there are competing goals of reduced head/disk friction andminimum transducer flying height.

Conventional practices for addressing these apparent competingobjectives involve providing a magnetic disk with a roughened recordingsurface to reduce the head/disk friction by techniques generallyreferred to as “texturing.” Conventional texturing techniques involvemechanical polishing or laser texturing the surface of a disk substrateto provide a texture thereon prior to subsequent deposition of layers,such as an underlayer, a magnetic layer, a protective overcoat, and alubricant topcoat, wherein the textured surface on the substrate isintended to be substantially replicated in the subsequently depositedlayers. The surface of an underlayer can also be textured, and thetexture substantially replicated in subsequently deposited layers.

Conventional longitudinal recording media typically comprise asubstrate, such as aluminum (Al) or an Al alloy, e.g.,aluminum-magnesium (Al—Mg) alloy, plated with a layer of amorphousnickel-phosphorus (NiP). Alternative substrates include glass, ceramic,glass-ceramic, and polymeric materials and graphite. The substratetypically contains sequentially deposited on each side thereof at leastone underlayer, such as chromium (Cr) or a Cr-alloy, e.g., chromiumvanadium (CrV), a cobalt (Co)-base alloy magnetic layer, a protectiveovercoat typically containing carbon, and a lubricant. The underlayer,magnetic layer and protective overcoat, are typically sputter depositedin an apparatus containing sequential deposition chambers. Aconventional Al-alloy substrate is provided with a NiP plating,primarily to increase the hardness of the Al substrate, serving as asuitable surface to provide a texture, which is substantially reproducedon the disk surface.

In accordance with conventional practices, a lubricant topcoat isuniformly applied over the protective overcoat to prevent wear betweenthe disk and head interface during drive operation. Excessive wear ofthe protective overcoat increases friction between the head and disk,thereby causing catastrophic drive failure. Excess lubricant at thehead-disk interface causes high stiction between the head and disk. Ifstiction is excessive, the drive cannot start and catastrophic failureoccurs. Accordingly, the lubricant thickness must be optimized forstiction and friction.

A conventional material employed for the lubricant topcoat comprises aperfluoro polyether (PFPE) which consists essentially of carbon,fluorine and oxygen atoms. The lubricant is typically dissolved in anorganic solvent, applied and bonded to the carbon overcoat of themagnetic recording medium by techniques such as dipping, buffing,thermal treatment, ultraviolet (UV) irradiation and soaking. Asignificant factor in the performance of a lubricant topcoat is thebonded lube ratio which is the ratio of the amount of lubricant bondeddirectly to the carbon overcoat of the magnetic recording medium to theamount of lubricant bonded to itself or to a mobile lubricant.Desirably, the bonded lube ratio should be between 0.3 to 0.7 (e.g.about 0.5 (50%)) to realize a meaningful improvement in stiction andwear performance of the resulting magnetic recording medium.

The escalating requirements for high areal recording density imposeincreasingly greater requirements on thin film magnetic recording mediain terms of coercivity, stiction, squareness, medium noise and narrowtrack recording performance. In addition, increasingly high arealrecording density and large-capacity magnetic disks require smallerflying heights, i.e., the distance by which the head floats above thesurface of the disk in the CSS drive (head-disk interface). Forconventional media design, a decrease in the head to media spacingincreases stiction and drive crash, thereby imposing an indispensablerole on the carbon-protective overcoat.

There are various types of carbon, some of which have been employed fora protective overcoat in manufacturing a magnetic recording medium. Suchtypes of carbon include hydrogenated carbon, graphitic carbon orgraphite, and nitrogenated carbon or carbon nitride andhydrogen-nitrogenated carbon. These types of carbon are well known inthe art and, hence, not set forth herein in great detail.

Generally, hydrogenated carbon or amorphous hydrogenated carbon has ahydrogen concentration of about 5 at. % to about 40 at. %, typicallyabout 20 at. % to about 30 at. %. Hydrogenated carbon has a lowerconductivity due to the elimination of the carbon band-gap states byhydrogen. Hydrogenated carbon also provides effective corrosionprotection to an underlying magnetic layer. Amorphous carbon nitride,sometimes referred to as nitrogenated carbon, generally has a nitrogento hydrogen concentration ratio of about 5:20 to about 30:0.Hydrogen-nitrogenated carbon generally has a hydrogen to nitrogenconcentration ratio of about 30:10 to 20:10 (higher concentration ofhydrogen than nitrogen). Amorphous (a) hydrogen-nitrogenated carbon canbe represented by the formula a-CH_(x)N_(y), wherein “x” is about 0.05(5.0 at. %) to about 0.20 (20 at. %), such as about 0.1 (10 at. %) toabout 0.2 (20 at. %), and “y” about 0.03 (3.0 at. %) to about 0.30 (30at. %), such as about 0.03 (3.0 at. %) to about 0.07 (7.0 at. %). Aparticularly suitable composition is a-CH_(0.15)N_(0.05). Graphiticcarbon or graphite contains substantially no hydrogen and nitrogen.

The drive for high areal recording density and, consequently, reducedflying heights, challenges the capabilities of conventionalmanufacturing practices. For example, a suitable protective overcoatmust be capable of preventing corrosion of the underlying magneticlayer, which is an electrochemical phenomenon dependent upon factorssuch as environmental conditions, e.g., humidity and temperature. Inaddition, a suitable protective overcoat must prevent migration of ionsfrom underlying layers into the lubricant topcoat and to the surface ofthe magnetic recording medium forming defects such as asperities. Aprotective overcoat must also exhibit the requisite surface for wearresistance, lower stiction, and some polarity to enable bonding theretoof a lubricant topcoat in an adequate thickness.

Furthermore, as the head-disk interface decreases to less than about 1μinch, it is necessary to reduce the thickness of the carbon-containingprotective overcoat to below about 100 Å to improve performance of themagnetic recording medium and reduce the spacing loss between theread/write head and magnetic recording medium surface. However, when thethickness of the carbon-containing protective overcoat is reduced tobelow about 100 Å, corrosion protection is adversely affected. Inaddition, head crash is encountered because it exhibits very poortribological properties and low reliability. Most GMR and MR mediaovercoats comprise a single layer of carbon material, such as amorphoushydrogenated carbon or amorphous nitrogenated carbon and exhibitadequate reliability at a thickness of about 125 Å to about 250 Å.However, as the thickness of the carbon-containing overcoat is reducedto below about 100 Å, head crash occurs, presumably because of lowerwear resistance and the discontinuities formed in the sputter depositedlayer.

Prior attempts have been made to reduce the thickness and increase thedensity of carbon-containing protective overcoats. Such techniquesinclude plasma-enhanced chemical vapor deposition and ion-beamdeposition. However, such prior attempts have met with adisadvantageously high defect count and lack of manufacturingfeasibility.

Prabhakara et al., in U.S. Pat. No. 5,855,746, discloses a magneticrecording medium having a plurality of carbon-containing protectivelayers with an outer nitrogen-containing layer, wherein nitrogen isexcluded from the initial carbon deposition for improved coercivity.Hwang et al., in U.S. Pat. No. 5,785,825, disclose a dual phase carbonovercoat including an initial amorphous carbon film on a magnetic layerand a doped amorphous carbon film sputter deposited on the amorphouscarbon film. Lal et al., in U.S. Pat. No. 5,714,044, disclose a magneticrecording medium containing first and second carbon overcoats, whereinthe second carbon overcoat is deposited under a nitrogen-containingatmosphere. Onodera, in U.S. Pat. No. 5,607,783, discloses a magneticrecording medium containing single or plural carbon-containingprotective layers with increasing hydrogen content. Nagao et al., inU.S. Pat. No. 4,869,797 disclose a method of sputter depositing a carbonprotective layer with a bias voltage of −10V to −100V applied in thevicinity of the support and magnetic layer.

In copending U.S. Pat. application Ser. No. 09/065,014 filed on Apr. 21,1998 a multilayer protective overcoat is disclosed which contains afirst hydrogenated carbon protective overcoat and a second protectiveovercoat of graphitic carbon or carbon nitride. In copending U.S. patentapplication Ser. No. 09/161,278 filed on Sep. 28, 1998 a magneticrecording medium is disclosed containing an amorphous carbon overcoatand a nitrogenated carbon overcoat deposited thereon.

There exists a continuing need for a magnetic recording mediumcomprising a protective overcoat capable of satisfying the imposingdemands for high areal recording density, reduced head-disk interfaceand corrosion protection. There also exists a particular need for amagnetic recording medium having a protective overcoat with a thicknessof less than about 100 Å affording superior corrosion protection,exhibiting excellent tribological properties at very low glide heightsand having long term durability.

DISCLOSURE OF THE INVENTION

An advantage of the present invention is an effective magnetic recordingmedium comprising a protective overcoat having a thickness less thanabout 100 Å, providing superior corrosion protection, exhibitingexcellent tribological properties at very low glide heights and havinglong term durability.

Additional advantages and other features of the present invention willbe set forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following disclosure or may be learned from thepractice of the present invention. The advantages of the presentinvention may be realized and obtained as particularly pointed out inthe appended claims.

According to the present invention, the foregoing and other advantagesare achieved in part by a magnetic recording medium comprising: amagnetic layer; a first protective layer comprising hydrogenated carbonhaving a density of at least about 1.9 on the magnetic layer; and asecond protective layer comprising nitrogen-doped hydrogenated carbon onthe first protective layer.

Another aspect of the present invention is a method of manufacturing amagnetic recording medium, the method comprising: sputter depositing afirst protective layer on a magnetic layer overlying a non-magneticsubstrate while applying a direct current (DC) bias to the substrate,the deposited first protective layer comprising hydrogenated carbon andhaving a density of at least about 1.9; and sputter depositing a secondprotective layer on the first protective layer, the second protectivelayer comprising nitrogen-doped hydrogenated carbon.

Embodiments of the present invention comprise depositing the secondprotective layer while applying a DC bias to the substrate such that thesecond protective layer has a density of at least about 1.85.Embodiments of the present invention further comprise depositing thefirst and second protective layers at a combined thickness of less than100 Å, wherein the thickness of the first protective layer is less thanthe thickness of the second protective layer. For example, the thicknessof the first protective layer can be about 20% to about 40% of thecombined thickness and the thickness of the second protective layer canbe about 60% to about 80% of the combined thickness. Embodiments of thepresent invention further comprise a programmable bias function, whereinthe first and second protective layers are deposited at a substantiallyconstant DC bias applied to the substrate as a single step function.Other embodiments of the present invention comprise depositing the firstand second protective layers by applying a multistep function whereinthe DC bias is reduced from a first value to a second value during thedeposition process, e.g., at approximately midpoint, and depositing thefirst and second protective layers while applying the DC bias as arampdown function wherein it is continuously reduced throughoutdeposition.

A further aspect of the present invention is a computer-readable mediumbearing instructions for sputter depositing layers on a substrate, theinstructions arranged, when executed by one or more processors, to causethe one or more processors to control a sputtering system to perform themanipulative steps of the inventive methodology disclosed herein.

Additional advantages of the present invention will become readilyapparent to those having ordinary skill in the art from the followingdetailed description, wherein the embodiments of the present inventionare described, simply by way of illustration of the best modecontemplated for carrying out the present invention. As will berealized, the present invention is capable of other and differentembodiments, and its several details are capable of modifications invarious obvious respects, all without departing from the presentinvention. Accordingly, the drawings and description are to be regardedas illustrative in nature, and not as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates a magnetic recording medium inaccordance with an embodiment of the present invention.

FIG. 2 is a graph showing the change in density measured on the uppernitrogen-doped hydrogenated carbon layer of the inventive dual sputterdeposited layers as a function of bias voltage.

FIG. 3 is a graph showing cobalt intensity as a function of biasvoltage.

FIG. 4 is a graph showing oxygen content as a function of bias voltage.

FIG. 5 is a graph showing binding energy as a function of bias voltage.

FIG. 6 illustrates an example of a programmable bias function inaccordance with an embodiment of the present invention.

FIG. 7 depicts a block diagram of a computer system configured forcontrolling sputter deposition in accordance with an embodiment of thepresent invention.

DESCRIPTION OF THE INVENTION

The present invention enables the manufacture of magnetic recordingmedia containing a dual protective overcoat system having a combinedthickness less than about 100 Å exhibiting excellent tribologicalproperties at a very low glide height, e.g., below about 1 μinch, longterm durability and superior corrosion resistance. Embodiments of thepresent invention, therefore, enable the manufacture of MR and GMRmagnetic recording media with improved magnetic recording performanceand reduced spacing loss between the read/write head and magneticrecording surface by reducing the overcoat thickness to even less than75 Å, e.g., less than about 45 Å.

Prior attempts to reduce the overall protective overcoat thickness toless than 100 Å to optimize magnetic performance sacrificed corrosionresistance, invited high defect counts and resulted in lack ofmanufacturing feasibility. In accordance with the present invention, adual protective overcoat system is provided at a total thickness of lessthan 100 Å for optimum magnetic performance and superior corrosionresistance. In accordance with embodiments of the present invention, afirst relatively thin protective layer is deposited on the magneticlayer by sputter deposition employing a relatively high direct current(DC) bias on the substrate, e.g., a bias of about 200V to about 400V,e.g., 300V to 400V. The relatively high substrate bias applied duringsputter deposition of the first protective layer results in a protectivelayer having a density greater than that which would normally resultfrom employing no or less substrate bias during deposition. For example,in depositing a first protective layer of hydrogenated carbon inaccordance with conventional practices without a substrate bias or witha low substrate bias, the deposited layer would typically exhibit adensity of about 1.7. However, in accordance with embodiments of thepresent invention, a relatively high substrate bias is applied duringsputter deposition resulting in a hydrogenated carbon layer exhibiting adensity of about 1.9 to about 2. A second relatively thick layer is thendeposited on the first layer. The second layer can containnitrogen-doped hydrogenated carbon. The use of a second nitrogen-dopedhydrogenated carbon layer provides better CSS performance at thehead-disc interface avoiding wear on the disk and the generation ofdebris. The inclusion of nitrogen in the second or upper protectiveovercoat prevents the generation of debris and, hence, minimizesmaintenance and improves longevity.

The formation of a highly dense first protective layer on the magneticlayer substantially prevents migration of components from the magneticlayer, e.g., cobalt and nickel. The exact operative mechanism enablingthe formation of a dense protective coating by application of arelatively high substrate bias is not known with certainty. However, itis believed that the application of a relatively high substrate biasknocks off loose particles, such as carbon particles, thereby preventinga clean surface for deposition and growth of a denser layer than thatdeposited on loose particles. The second protective layer can, but neednot, be deposited at a relatively high substrate bias and typicallyexhibits a density which is equal or no less than 0.05 less than thedensity of the first protective layer.

Embodiments of the present invention comprise depositing a first layerof hydrogenated carbon having a hydrogen concentration of about 10 toabout 30 at. %, such as about 15 to about 25 at. %, e.g., about 20 at.%. The second or top protective layer can comprise nitrogen-dopedhydrogenated carbon containing about 2 to about 8 at. % nitrogen, suchas about 4 to about 6 at. % nitrogen, and about 10 to about 20 at. %hydrogen, e.g., about 12 to about 14 at. % hydrogen. The relativethickness of the first and second layers can be optimized in aparticular situation. It was found suitable to deposit the first andsecond protective layers such that the first layer has a thickness ofabout 20% to about 40% of the overall thickness, where the second layerhas a thickness of about 60% to about 80% of the overall thickness ofthe protective layers.

Magnetic recording media in accordance with the present invention cancomprise any conventional substrate, such as NiP/Al or an NiP/Al alloysubstrate, Al or an Al alloy substrate, or a glass, ceramic,glass-ceramic or polymeric substrate. The present invention can beimplemented employing any of the various seedlayers, underlayers,magnetic layers and lubricant topcoats conventionally employed inmanufacturing magnetic recording media. For example, embodiments of thepresent invention comprise the use of a Cr or Cr alloy underlayer orunderlayers, Co-alloy magnetic layers and (PFPE) lubricants for enhancedurability.

An embodiment of the present invention is schematically illustrated inFIG. 1 and comprises a substrate 10, e.g., Al, an Al alloy, a polymer, aglass, a ceramic, or a glass-ceramic, having sequentially deposited oneach side thereof an underlayer 11 and a magnetic layer 12, e.g., acobalt alloy, on underlayer 11.

In accordance with the present invention, a first magnetic layer 13,e.g., a hydrogenated carbon layer, is deposited on magnetic layer 12 ata high substrate bias, e.g., about 300V. The first protective layer 13typically has a density of about 1.9 to about 2. A second protectivelayer 14 is then deposited on first protective layer 13. Secondprotective layer 14 can comprise nitrogen-doped hydrogenated carbon. Alubricant topcoat 15 is then applied. Although not illustrated,embodiments of the present invention can comprise conventional seedlayers and composite underlayers. It should be understood that thelayers 11, 12, 13, 14, 15 are sequentially deposited on both sides ofsubstrate 10 in a conventional manner.

The combined thicknesses of protective overcoats 13 and 14 illustratedin FIG. 1 is less than 100 Å for optimum tibological performance. Inaddition, due to the high density and hardness, the protective overcoatsystem of the present invention exhibits superior corrosion resistance,preventing migration of ions from underlying layers.

Testing was conducted at various substrate biases to illustrate theimpact of bias on the substrate during sputter deposition of a dualprotective overcoat system in accordance with the present invention. Theresults are reported in FIG. 2 and illustrate the increase in averagedensity measured on the upper nitrogen-doped hydrogenated carbon layerof an inventive sputtered dual layer protective overcoat system withincreasing substrate bias.

FIG. 3 confirms that the denser films deposited at a high substrate biasexhibit reduced corrosion. Manifestly, the higher substrate biasvoltages contributed to superior surface coverage of the magnetic layerand reduced cobalt counts.

Another advantage of the present invention is a reduction in oxygenconcentration in the protective overcoat. Oxygen is known to bedetrimental for inducing corrosion. Testing conducted demonstratedreduced oxygen intensity with increased substrate bias during sputterdepositing a dual overcoat system in accordance with the presentinvention as shown in FIG. 4.

Another advantage of the present invention is increased durabilityattendant upon increased substrate bias. FIG. 5 illustrates the increaseof the sp3 binding characteristics among carbon atoms, thereby improvingthe durability of the inventive dual protective overcoat system. Theincrease in density, reduction of oxygen concentration and increasedbinding strength contribute to improved corrosion resistance.

In an embodiment of the present invention, a programmable bias isemployed during the deposition of the dual carbon layers. Theprogrammable bias can be applied as a multistep function, rampupfunction or rampdown function. The programmable bias feature enablesdepositing a high bias carbon for the bottom layer employing either stepor rampdown function and depositing a lower bias carbon for a top layeremploying a rampdown bias function. Thus, the programmable bias featureadvantageously enables deposition of the harder carbon layer as thebottom layer while depositing a less dense film as the top layer. Inthis way, the protective overcoat of the present invention is optimizedso that the bottom denser film provides superior corrosion protectionwhile the top less dense layer provides a friendly surface for thehead-disc interface.

A programmable bias can be applied at each station and can include: (a)a high bias step function for sputter depositing the first carbon layerwith increased density and superior corrosion resistance, employing abias of about 250V to about 400V; and (b) a low, step bias or rampdownfunction for the second carbon layer, employing a step bias in the rangeof about 100 V to about 250V and up to 50V to complete deposition.

An example of a programmable bias function in accordance with anembodiment of the present invention is illustrated in FIG. 6. Themultiple step function shift occurs about about mid point of thedeposition for the particular layer.

Another aspect of the present invention relates to the use of computersystem to control a sputtering system for sequentially depositing layersin manufacturing a magnetic recording medium. FIG. 7 depicts a generalpurpose computer system 100 configured to execute a software forcontrolling sputtering system 70. The computer system 100 contains acomputer 102, one or more display devices 104, and one or more inputdevices 106. The computer 102 contains a central processing unit (CPU)108 such as an Intel 486 microprocessor, a memory 110 and assertedsupport circuitry 112 such as a math co-processor, power supply, and thelike. Such computer systems are commonly known as personal computers,however, the present invention is not limited to personal computers andmay, in fact, be implemented on workstations, minicomputer, mainframes,and supercomputers. The input devices 106 used with such computersinclude a keyboard, a mouse, trackball and the like. The display devices104 include computer monitors, printers and plotters.

Computer system 100 also includes a memory 110, such as a random accessmemory (RAM) or other dynamic storage device for storing information andinstructions to be executed by CPU 108. Memory 110 also may be used forstoring temporary variables or other intermediate information duringexecution of instructions to be executed by CPU 108. Memory 110 furtherincludes a read only memory (ROM) or other static storage device forstoring static information and instructions for CPU 108. Memory 110 mayalso include a storage device, such as a magnetic disk or optical disk,provided for storing information and instructions.

The interface 124 allows the computer system 100 to communicate with thesputtering system 70, specifically with sputtering controller 154. Thesputtering system 70 could comprise an in-line type of sputtering systemcomprising sequential deposition and, when appropriate, heatingchambers. In the embodiment depicted in FIG. 7, sputtering system 70comprises, inter alia, conveyor 71 on which a substrate is placed as itis conveyed past various sputter depositing chambers, e.g., chamber 74for depositing an underlayer chamber 75 for depositing a magnetic layer76 for depositing the first protective layer and chamber 77 fordepositing the second protective layer. Bias rings 72 and 73 arepositioned to provide a voltage on the substrate while sputterdepositing the first and second protective layers which can also beimplemented in a single deposition chamber. Sputtering system controller154 controls motion of conveyor 71 and the various sputtering parametersand conditions.

According to an embodiment of the present invention, sputtering isprovided by computer system 100 controlling sputtering system 70 inresponse to CPU 108 executing one or more sequences of one or moreinstructions contained in a program 120 in memory 110. For example,instructions may be read into main memory from another computer-readablemedium, such as a storage device. Execution of the sequences ofinstructions contained in memory 110 causes CPU 108 to perform theprocess steps described herein. One or more processors in amulti-processing arrangement may also be alternative embodiments,hard-wired circuitry may be used in place of or in combination withsoftware instructions to implement the invention. Thus, embodiments ofthe invention are not limited to any specific combination of hardwarecircuitry and software.

The term “computer-readable medium” as used herein refers to any mediumthat participates in providing instructions to CPU 108 for execution.Such a medium may take many forms, including but not limited to,non-volatile media, volatile media, and transmission media. Non-volatilemedia include, for example, optical or magnetic disks, such as a storagedevice. Volatile media include dynamic memory, such as a main memory.Transmission media include coaxial cables, copper wire and fiber optics,including the wires that comprise a system bus. Transmission media canalso take the form of acoustic or light waves, such as those generatedduring radio frequency (RF) and infrared (IR) data communications.Common forms of computer-readable media include, for example, a floppydisk, a flexible disk, hard disk, magnetic tape, any other magneticmedium, a CD-ROM, DVD, any other optical medium, punch cards, papertape, any other physical medium with patterns of holes, a RAM, a PROM,and EPROM, a FLASH-EPROM, any other memory chip or cartridge, a carrierwave as described hereinafter, or any other medium from which a computercan read.

Various forms of computer readable media may be involved in carrying oneor more sequences of one or more instructions to CPU 108 for execution.For example, the instructions may initially be borne on a magnetic diskof a remote computer. The remote computer can load the instructions intoits dynamic memory and send the instructions over a telephone line usinga modem. A modem (not shown) local to computer system 100 can receivethe data on the telephone line and use an infrared transmitter toconvert the data to an infrared signal. An infrared detector as an inputdevice 106 can receive the data carried in the infrared signal and placethe data on the system bus, which carries the data to memory 110, fromwhich CPU 108 retrieves and executes the instructions. The instructionsreceived at memory 110 may optionally be stored on storage device eitherbefore or after execution by CPU 108.

The present invention provides magnetic recording media having aprotective carbon overcoat at a thickness significantly less than 100 Å,e.g. less than 45 Å, for MR and MRG recording with optimum magneticperformance and improved corrosion resistance by sputter depositing afirst protective carbon overcoat under a high substrate bias forincreased density and hardness, reduced oxygen concentration andincreased sp3 binding characteristics for improved corrosion resistance.Magnetic recording media in accordance with the present inventionexhibit excellent tribological properties at very low glide heights,e.g. less than about 1 μinch, with long term durability.

The present invention can be advantageously employed to produce any ofvarious types of magnetic recording media, including thin film disks.The present invention is particularly applicable in producing high arealrecording density magnetic recording media requiring a low flyingheight.

Only the preferred embodiment of the present invention and but a fewexamples of its versatility are shown and described in the presentdisclosure. It is to be understood that the present invention is capableof use in various other combinations and environments and is capable ofchanges or modifications within the scope of the inventive concept asexpressed herein.

What is claimed is:
 1. A magnetic recording medium comprising: a magnetic layer; a first protective layer having a first thickness and comprising hydrogenated carbon and having a density of at least about 1.9 on the magnetic layer; and a second protective layer comprising nitrogen-doped hydrogenated carbon on the first protective layer, the second protective layer having a second thickness greater than the first thickness.
 2. The magnetic recording medium according to claim 1, wherein the second protective layer has a density less than that of the first protective layer.
 3. The magnetic recording medium according to claim 1, wherein: the first protective layer comprises about 10 to about 30 at. % hydrogen; and the second protective layer comprises about 10 to about 20 at. % hydrogen and about 2 to about 8 at. % nitrogen.
 4. The magnetic recording medium according to claim 1, wherein the first and second protective layers have a combined thickness of less than about 100 Å.
 5. The magnetic recording medium according to claim 4, wherein: the first protective layer has a thickness of about 20% to about 40% of the combined thickness; and the second protective layer has a thickness of about 60% to about 80% of the combined thickness.
 6. The magnetic recording medium according to claim 1, further comprising: a non-magnetic substrate; an underlayer on the non-magnetic substrate; the magnetic layer on the underlayer; the first protective layer on the magnetic layer; and a lubricant topcoat on the second protective layer. 